using System;

using Org.BouncyCastle.Crypto.Parameters;

namespace Org.BouncyCastle.Crypto.Engines
{
	/**
	* a class that provides a basic SKIPJACK engine.
	*/
	public class SkipjackEngine
		: IBlockCipher
	{
		const int BLOCK_SIZE = 8;

		static readonly short [] ftable =
		{
			0xa3, 0xd7, 0x09, 0x83, 0xf8, 0x48, 0xf6, 0xf4, 0xb3, 0x21, 0x15, 0x78, 0x99, 0xb1, 0xaf, 0xf9,
			0xe7, 0x2d, 0x4d, 0x8a, 0xce, 0x4c, 0xca, 0x2e, 0x52, 0x95, 0xd9, 0x1e, 0x4e, 0x38, 0x44, 0x28,
			0x0a, 0xdf, 0x02, 0xa0, 0x17, 0xf1, 0x60, 0x68, 0x12, 0xb7, 0x7a, 0xc3, 0xe9, 0xfa, 0x3d, 0x53,
			0x96, 0x84, 0x6b, 0xba, 0xf2, 0x63, 0x9a, 0x19, 0x7c, 0xae, 0xe5, 0xf5, 0xf7, 0x16, 0x6a, 0xa2,
			0x39, 0xb6, 0x7b, 0x0f, 0xc1, 0x93, 0x81, 0x1b, 0xee, 0xb4, 0x1a, 0xea, 0xd0, 0x91, 0x2f, 0xb8,
			0x55, 0xb9, 0xda, 0x85, 0x3f, 0x41, 0xbf, 0xe0, 0x5a, 0x58, 0x80, 0x5f, 0x66, 0x0b, 0xd8, 0x90,
			0x35, 0xd5, 0xc0, 0xa7, 0x33, 0x06, 0x65, 0x69, 0x45, 0x00, 0x94, 0x56, 0x6d, 0x98, 0x9b, 0x76,
			0x97, 0xfc, 0xb2, 0xc2, 0xb0, 0xfe, 0xdb, 0x20, 0xe1, 0xeb, 0xd6, 0xe4, 0xdd, 0x47, 0x4a, 0x1d,
			0x42, 0xed, 0x9e, 0x6e, 0x49, 0x3c, 0xcd, 0x43, 0x27, 0xd2, 0x07, 0xd4, 0xde, 0xc7, 0x67, 0x18,
			0x89, 0xcb, 0x30, 0x1f, 0x8d, 0xc6, 0x8f, 0xaa, 0xc8, 0x74, 0xdc, 0xc9, 0x5d, 0x5c, 0x31, 0xa4,
			0x70, 0x88, 0x61, 0x2c, 0x9f, 0x0d, 0x2b, 0x87, 0x50, 0x82, 0x54, 0x64, 0x26, 0x7d, 0x03, 0x40,
			0x34, 0x4b, 0x1c, 0x73, 0xd1, 0xc4, 0xfd, 0x3b, 0xcc, 0xfb, 0x7f, 0xab, 0xe6, 0x3e, 0x5b, 0xa5,
			0xad, 0x04, 0x23, 0x9c, 0x14, 0x51, 0x22, 0xf0, 0x29, 0x79, 0x71, 0x7e, 0xff, 0x8c, 0x0e, 0xe2,
			0x0c, 0xef, 0xbc, 0x72, 0x75, 0x6f, 0x37, 0xa1, 0xec, 0xd3, 0x8e, 0x62, 0x8b, 0x86, 0x10, 0xe8,
			0x08, 0x77, 0x11, 0xbe, 0x92, 0x4f, 0x24, 0xc5, 0x32, 0x36, 0x9d, 0xcf, 0xf3, 0xa6, 0xbb, 0xac,
			0x5e, 0x6c, 0xa9, 0x13, 0x57, 0x25, 0xb5, 0xe3, 0xbd, 0xa8, 0x3a, 0x01, 0x05, 0x59, 0x2a, 0x46
		};

		private int[] key0, key1, key2, key3;
		private bool encrypting;

		/**
		* initialise a SKIPJACK cipher.
		*
		* @param forEncryption whether or not we are for encryption.
		* @param parameters the parameters required to set up the cipher.
		* @exception ArgumentException if the parameters argument is
		* inappropriate.
		*/
		public void Init(
			bool				forEncryption,
			ICipherParameters	parameters)
		{
			if (!(parameters is KeyParameter))
				throw new ArgumentException("invalid parameter passed to SKIPJACK init - " + parameters.GetType().ToString());

			byte[] keyBytes = ((KeyParameter)parameters).GetKey();

			this.encrypting = forEncryption;
			this.key0 = new int[32];
			this.key1 = new int[32];
			this.key2 = new int[32];
			this.key3 = new int[32];

			//
			// expand the key to 128 bytes in 4 parts (saving us a modulo, multiply
			// and an addition).
			//
			for (int i = 0; i < 32; i ++)
			{
				key0[i] = keyBytes[(i * 4) % 10] & 0xff;
				key1[i] = keyBytes[(i * 4 + 1) % 10] & 0xff;
				key2[i] = keyBytes[(i * 4 + 2) % 10] & 0xff;
				key3[i] = keyBytes[(i * 4 + 3) % 10] & 0xff;
			}
		}

		public string AlgorithmName
		{
			get { return "SKIPJACK"; }
		}

		public bool IsPartialBlockOkay
		{
			get { return false; }
		}

		public int GetBlockSize()
		{
			return BLOCK_SIZE;
		}

		public int ProcessBlock(
			byte[]	input,
			int		inOff,
			byte[]	output,
			int		outOff)
		{
			if (key1 == null)
				throw new InvalidOperationException("SKIPJACK engine not initialised");
			if ((inOff + BLOCK_SIZE) > input.Length)
				throw new DataLengthException("input buffer too short");
			if ((outOff + BLOCK_SIZE) > output.Length)
				throw new DataLengthException("output buffer too short");

			if (encrypting)
			{
				EncryptBlock(input, inOff, output, outOff);
			}
			else
			{
				DecryptBlock(input, inOff, output, outOff);
			}

			return BLOCK_SIZE;
		}

		public void Reset()
		{
		}

		/**
		* The G permutation
		*/
		private int G(
			int     k,
			int     w)
		{
			int g1, g2, g3, g4, g5, g6;

			g1 = (w >> 8) & 0xff;
			g2 = w & 0xff;

			g3 = ftable[g2 ^ key0[k]] ^ g1;
			g4 = ftable[g3 ^ key1[k]] ^ g2;
			g5 = ftable[g4 ^ key2[k]] ^ g3;
			g6 = ftable[g5 ^ key3[k]] ^ g4;

			return ((g5 << 8) + g6);
		}

		public int EncryptBlock(
			byte[]      input,
			int         inOff,
			byte[]      outBytes,
			int         outOff)
		{
			int w1 = (input[inOff + 0] << 8) + (input[inOff + 1] & 0xff);
			int w2 = (input[inOff + 2] << 8) + (input[inOff + 3] & 0xff);
			int w3 = (input[inOff + 4] << 8) + (input[inOff + 5] & 0xff);
			int w4 = (input[inOff + 6] << 8) + (input[inOff + 7] & 0xff);

			int k = 0;

			for (int t = 0; t < 2; t++)
			{
				for(int i = 0; i < 8; i++)
				{
					int tmp = w4;
					w4 = w3;
					w3 = w2;
					w2 = G(k, w1);
					w1 = w2 ^ tmp ^ (k + 1);
					k++;
				}

				for(int i = 0; i < 8; i++)
				{
					int tmp = w4;
					w4 = w3;
					w3 = w1 ^ w2 ^ (k + 1);
					w2 = G(k, w1);
					w1 = tmp;
					k++;
				}
			}

			outBytes[outOff + 0] = (byte)((w1 >> 8));
			outBytes[outOff + 1] = (byte)(w1);
			outBytes[outOff + 2] = (byte)((w2 >> 8));
			outBytes[outOff + 3] = (byte)(w2);
			outBytes[outOff + 4] = (byte)((w3 >> 8));
			outBytes[outOff + 5] = (byte)(w3);
			outBytes[outOff + 6] = (byte)((w4 >> 8));
			outBytes[outOff + 7] = (byte)(w4);

			return BLOCK_SIZE;
		}

		/**
		* the inverse of the G permutation.
		*/
		private int H(
			int     k,
			int     w)
		{
			int h1, h2, h3, h4, h5, h6;

			h1 = w & 0xff;
			h2 = (w >> 8) & 0xff;

			h3 = ftable[h2 ^ key3[k]] ^ h1;
			h4 = ftable[h3 ^ key2[k]] ^ h2;
			h5 = ftable[h4 ^ key1[k]] ^ h3;
			h6 = ftable[h5 ^ key0[k]] ^ h4;

			return ((h6 << 8) + h5);
		}

		public int DecryptBlock(
			byte[]      input,
			int         inOff,
			byte[]      outBytes,
			int         outOff)
		{
			int w2 = (input[inOff + 0] << 8) + (input[inOff + 1] & 0xff);
			int w1 = (input[inOff + 2] << 8) + (input[inOff + 3] & 0xff);
			int w4 = (input[inOff + 4] << 8) + (input[inOff + 5] & 0xff);
			int w3 = (input[inOff + 6] << 8) + (input[inOff + 7] & 0xff);

			int k = 31;

			for (int t = 0; t < 2; t++)
			{
				for(int i = 0; i < 8; i++)
				{
					int tmp = w4;
					w4 = w3;
					w3 = w2;
					w2 = H(k, w1);
					w1 = w2 ^ tmp ^ (k + 1);
					k--;
				}

				for(int i = 0; i < 8; i++)
				{
					int tmp = w4;
					w4 = w3;
					w3 = w1 ^ w2 ^ (k + 1);
					w2 = H(k, w1);
					w1 = tmp;
					k--;
				}
			}

			outBytes[outOff + 0] = (byte)((w2 >> 8));
			outBytes[outOff + 1] = (byte)(w2);
			outBytes[outOff + 2] = (byte)((w1 >> 8));
			outBytes[outOff + 3] = (byte)(w1);
			outBytes[outOff + 4] = (byte)((w4 >> 8));
			outBytes[outOff + 5] = (byte)(w4);
			outBytes[outOff + 6] = (byte)((w3 >> 8));
			outBytes[outOff + 7] = (byte)(w3);

			return BLOCK_SIZE;
		}
	}

}
